Digital rf tag

ABSTRACT

An RF tag is provided to communicate with an interogating source in which the tag has programmability and flexibility to uplink data to multiple platforms. As such the RF tag functions as a miniature programmable transceiver capable of communicating with a plurality of different platforms each having different waveform characteristics. With well-controlled spectral characteristics due to stored waveforms and the use of specialized direct digital up and down conversion techniques, data rates up to 256 kbps are achievable. The tag is thus capable of converting microwave signals directly to digital inputs, and the transmitter generates microwave signals directly from digital outputs. Flexible digital processing also allows a throughput of 900 BOPS when using field programmable gate arrays.

FIELD OF INVENTION

The present invention relates to transceivers and more particularly toradio frequency (RF) tags.

BACKGROUND OF THE INVENTION

An RF tag is a miniature transceiver capable of communicating with aremote platform such as an aircraft or a satellite. Existing RF tags arefairly large, power-hungry, and are usually capable of operating withonly a single overflying platform. What is therefore needed is a small,rugged device, capable of battery-powered operation for long periods oftime, and with programmability to allow operation with many differentplatforms for which it is to communicate. Also needed is an RF tag forcovert use so that troops wearing the RF tag can operate undetected. Forcommercial use, there is a requirement for vehicle, package andpersonnel tracking; as well as a need for a convenient light weightsearch and rescue device which can be worn.

SUMMARY OF THE INVENTION

The subject digital RF tag is a general purpose, programmabletransceiver which radar source in such a way that the signal is hiddenin the radar ground clutter. This requires special modulationcharacteristics and attention to spurious emissions. As a feature of thesubject invention, the tag is programmable which means that it cancommunicate with a variety of radio frequency (RF) waveforms emittedfrom a source of interrogating energy.

As will be seen, the subject digital RF tag may be interrogated by anykind of RF waveform based either on radar or a communications system. Akey advantage is that the tag allows the waveform characteristics to bestored digitally within the tag, thus enabling the tag to communicatewith an interrogating platform by modulating returned signals so thatthey have the same characteristics as the transmitted waveforms.Although this tag may be used in one preferred embodiment for radarwaveforms, those skilled in the art, however, will appreciate that itsextension to other RF waveforms, e.g., communications, is within thescope of the subject invention.

There are several techniques used by the digital RF tag which assist inthe operation of the tag. First is the use of digital up/downconversion. In one embodiment, on receive, an X-Band signal is directlydownconverted to digital by sampling in a fast track-and-hold device,the output of which is then converted from analog-to-digital form. Thetechnique is described for other applications in U.S. patent applicationSer. No. 10/323,060 filed Dec. 18, 2002, assigned to the assignee hereofand incorporated herein by reference.

On transmit, the digital signal is directly upconverted to the X-B andusing a digital-to-analog converter, followed by gating short pulsesfrom a return-to-zero device that tracks the waveform from thedigital-to-analog converter for short periods of time andreturns-to-zero its output for times in between the short pulses. Thisyields a pulse amplitude modulated waveform with harmonics in theX-Band. The pulse amplitude modulated waveform is filtered at thetransmitter with a band pass filter to filter out all but the X-Bandcomponents. Such a return-to-zero device is described in U.S. patentapplication Ser. No. 10/113,279 filed Apr. 1, 2002 assigned to theassignee hereof and incorporated herein by reference.

The direct digital up/downconversion not only eliminates the use oflocal oscillators which makes a tag detectable thus destroying itscovert operation, it also provides for efficient multiband operation.This is because the subject approach is based on sampled waveformharmonics and, therefore does not require local oscillators to supporteach band of interest.

Secondly, the digital RF tag establishes communications link modulationby fast-time convolution. Existing communications systems modulate thephase, frequency, and/or amplitude of a carrier in order to encodeinformation. The digital RF tag can perform this type of modulation butcan also perform a new type of modulation called fast-time convolution.In this method, the information is encoded onto the taps of aprogrammable convolver. A received radar waveform is then passed throughthis convolver and the resulting signal is transmitted. This approachprovides a means of modulating many bits of data onto a single radarpulse while not distorting the radar spectrum, thus achieving a highdata rate.

The above digital processing includes as a feature the matching of theconvolver tap spacing to the radar waveform bandwidth. The traditionalapproach is to use a convolver with a variable number of time delaysbetween taps. The approach used in the subject tag utilizes a fixedlength convolver preceded by a programmable decimator. The result ofprocessing decimated data through the fixed length convolver isequivalent to varying the time delays between the taps, thus toeliminate the problem of providing a bulky expensive variable lengthconvolver. This means that a small fixed length convolver can handlemany different interrogating waveforms and need not be specially adaptedfor each incoming waveform.

As to programmability, most of the operational features are programmableincluding communication protocols, authentication and interrogationprocedures, transmit power, message encoding algorithm, modulationcharacteristics, frequency, and bandwidth. Moreover, at the level ofsubmodules within the tag, one can use a meander line loaded antenna(MLA) at X-Band. This antenna type is described in U.S. Pat. No.5,790,080 issued Aug. 4, 1998, assigned to the assignee hereof andincorporated herein by reference, and has previously been used at lowerfrequencies.

Moreover, the technique described in U.S. Pat. No. 4,734,751 may be usedto achieve variable transmit gain and power. The RF transmit circuitryuses segmented dual gates for digitally controlled variable gain andvariable power with very high efficiency. While use of this techniquefor radars has been described, the use of this approach in acommunications application is new and is useful in lowering the returnedsignal to just that necessary for receipt by an over flying aircraft orsatellite. This minimizes detectability of the tag in covert oparations.

As to applications for the subject digital RF tag, the tag supportsautomated tracking. The tag has the potential to be used for automatedtracking of cargo, vehicles, or other objects. In this mode, a satellitesystem interrogates tags located on objects to be tracked, accepts thetag replies and updates a database of current locations. Authorizedusers then interrogate this database via internet access. Trackingpossible if a suitable airborne or space-based radar is employed as thecooperating platform. Also subcarriers from commercial radio stationscan be used for interrogating the tags.

The tag may also be used as a RF front end for universal routers. Inthis embodiment, a truly universal router handles links with fiber,copper, and RF links. In one embodiment, for the RF links, a universalrouter includes several tag modules which serve as broadband,programmable transceivers. This allows the router to be tailored to aparticular need by software rather than by developing new hardwaremodules.

Finally, the subject tag can be used as a Search-and-Rescue Transponder.The tag in this application is placed in lifejackets, life rafts,aircraft seat cushions, etc. The transponder is activated by contactwith water and then detected by search and rescue aircraft and shipswith X-Band radars to deliver much more information than is availablefrom standard Search & Rescue Transponders (SARTs) which is generallylimited to a series of dots on the radar screen going to thetransponder. No other information such as GPS position, identity of theindividual or the individual's particular problem or need is transmittedby these SARTs.

In summary, an RF tag is provided to communicate with an interrogatingsource in which the tag has programmability and flexibility to uplinkdata to multiple platforms. As such the RF tag functions as a miniatureprogrammable transceiver capable of communicating with a plurality ofdifferent platforms each having different waveform characteristics. Withwell-controlled spectral characteristics due to stored waveforms and theuse of specialized direct digital up and down conversion techniques,data rates up to 256 kbps are achievable. The tag is thus capable ofconverting microwave signals directly to digital inputs, and thetransmitter generates microwave signals directly from digital outputs.Flexible digital processing also allows a throughput of 900 BOPS whenusing field programmable gate arrays.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the subject invention will be betterunderstood in connection with the Detailed Description in conjunctionwith the Drawings, of which:

FIG. 1 is a diagrammatic representation of the utilization of thesubject RF tag interrogated by and communicating with an overflyingaircraft;

FIG. 2 is a diagrammatic representation of the chirped pulse produced bythe radar of the aircraft of FIG. 1;

FIG. 3 is a frequency versus amplitude graph showing the linear sweepfor the frequency of the chirped signal of FIG. 2;

FIG. 4 is a block diagram of the subject RF tag showing the utilizationof a DSP convolver and control processor having as one of its inputs aset of waveform characteristics;

FIG. 5 is a diagrammatic representation of the processing for the radarreceiver for the aircraft of FIG. 1, indicating the utilization of achirped waveform and the inverse thereof, with the multiplication ofthese two waveforms and integration over a given offset providing asharp spike indicating the range of the radar target to the radar;

FIG. 6 is a waveform illustrating the production of a sharp spike whichis the result of the multiplication of the two waveforms of FIG. 5, andintegration over an offset;

FIG. 7 is a waveform illustrating the recovering of a biphase-modulatedsignal;

FIG. 8 is a diagrammatic illustration of the relative amplitude of thedata message as opposed to the returned radar signal, illustrating thatthe data message is well submerged within the clutter and noise of thesignal returned to the interrogating radar;

FIG. 9 is a block diagram of the utilization of a decimator ahead of afixed tap convolver to permit the utilization of the fixed tap convolverto convolve a message signal with a received radar waveform from avariety of different sources;

FIG. 10 is a block diagram of the utilization of a track and holdcircuit for direct downconversion of the microwave signal without theutilization of local oscillators;

FIG. 11 is a waveform diagram illustrating the clock pulses coupled tothe track and hold circuit of FIG. 10, also illustrating the existenceof the radar pulse at the clock frequency corresponding to the microwaveregion of the electromagnetic spectrum;

FIG. 12 is a graph showing the result of the direct conversion down tobase band accomplished by multiplying the clock pulses of FIG. 11 by theradar pulse, thus to provide side bands about a DC reference;

FIG. 13 is a block diagram showing direct upconversion utilizing areturn-to-zero unit which tracks the waveform from a digital-to-analogconverted signal for a short period of time with zeros being providedfor the long period of time in between the short periods;

FIG. 14 is a waveform diagram illustrating the result of the utilizationof the return-to-zero unit of FIG. 13, showing the generation of awaveform envelope which is to be transmitted; and,

FIG. 15 is a waveform diagram illustrating the filtering out offrequencies below the microwave frequency clock pulse associated withthe clock of FIG. 10.

DETAILED DESCRIPTION

Referring now to FIG. 1, in one embodiment an RF tag 10 located on apiece of equipment or stand-alone is utilized to communicate with anoverlying aircraft 12, the radar of which emits pulses 14 to scanterrain 16 for the purpose of interrogating any tags which may beilluminated by the radar pulses. Alternatively terrestrial-basedtransmitters can be used to interrogate the subject tag.

When the radar pulses impinge on tag 10, a return signal 18 is embeddedwithin the returned pulse and is transmitted back to aircraft 12, withthe demodulation of the signal providing information that has beensupplied to the tag either by manual entry, reprogramming or, forinstance, through the connection of a GPS receiver to the tag. What thisprovides is a relatively low powered device which can be interrogated byan over flying aircraft or in fact a satellite as well as an unmannedair vehicle so that, for instance, troops can be located, packages canbe tracked, and information on the ground can be communicated back tothe radar interrogation source. This information is communicated throughthe use of an ultra small RF tag which is small enough to be embedded inclothing or unobtrusively placed on equipment.

Key to the ability to provide a covert device in an extremely smallpower stingy package, in the subject invention, the RF tag utilizes adigital up/down direct conversion technique, and a novel communicationslink modulation scheme involving fast time convolution, with the unititself being programmable for communication protocols, authenticationand integration procedures, as well as transmit power, message encoding,algorithms, modulation characteristics, frequency and bandwidth.

Key to the efficient use of the RF tag is the use of a digital signalprocessing, DSP, convolver which operates on the analog-to-digitalsampled interrogating pulse which it multiplies with the output from acontrol processor storing the information to be transmitted back. In oneembodiment, the subject tag provides a covert low observable signalembedded in the radar waveform bandwidth.

In a preferred embodiment, the modulation involves generating a pseudonoise code.

Referring to FIG. 2, it will be appreciated that what is transmittedfrom the over flying aircraft is a series of radar pulses 20 which inone embodiment include a chirped waveform 22 which is frequency chirpedas illustrated in FIG. 3 by waveform 24, in the illustrated embodimentgoing from a lower frequency to a higher frequency in a linear fashion.Chirped signals are in general used for better resolution and increasedrange as well as immunity to interference and noise.

Referring now to FIG. 4, in one embodiment the subject tag includes anRF receiver 26 coupled to an antenna 28. The output of the RF receiveris converted by an analog-to-digital converter 30 into a digitalrepresentation of the transmitted radar waveform. This is applied to adigital processor functioning as a convolver 32 which convolves theradar transmit waveform with the desired data message 34 available as anoutput from a control processor 36. In one embodiment, processor 36 ispreloaded with waveform characteristics as illustrated at 38. Thewaveform characteristics are the center frequency, chirp range, pulsewidth, and pulse repetition intervals or PRI of the expected incomingradar pulse. Note that the DSP convolver operates in several modes. Thefirst mode of operation is a scan mode in which the convolver scans theincoming signal as to its waveform characteristics. When these waveformcharacteristics are transmitted to control processor 36 on line 37 matchpreloaded waveform characteristics 38 then communication is initiated.

The modulation to be embedded into the returned signal can either befrom a GPS receiver 39, keyboard entered at 40 or from an external link42, all coupled to the control processor.

The output of the DSP convolver is a modulated waveform 49 involving apseudo noise code which is applied to transmitter 50 and is radiated outthrough an antenna 52 so that the RF tag acts a transponder whichtransmits back to the over flying communications entity the specificencoded information required.

Note, as mentioned above, that while the subject invention will bedescribed in connection with overflying vehicles, the subject RF tag canalso be interrogated by terrestrial sources such as radio stationsubcarriers and the like.

As will be appreciated, it is very important not to interfere with theradar's normal functions. In so doing it is important to understand, atleast initially, how the radar functions with chirped waveform signals.

Note also that in terms of programmability, the waveform characteristicscan be either directly preinstalled in processor 36 or can be varied viaoperator input by keyboard 40.

Referring now to FIG. 5, it will be appreciated that the radar itselftransmits a up-chirped waveform 54 which goes from a low frequency to ahigh frequency. The radar is also provided with a down-chirped replica56 of the waveform. When the two are multiplied together and averaged,the time convolution, as illustrated in FIG. 6, results in a spike 60which is used in the production of the radar image as the time of thespike determines the range of the reflecting radar target. The remainderof the signal which is received at the over flying radar is illustratedat 62 which includes noise and clutter. Because of the multiplying ofthe inverted and original chirped waveforms over a given offset,interfering signals such as jamming signals are reduced to a very lowlevel as illustrated by waveform 62.

Referring to FIG. 7, in one embodiment, if a bi-phase modulated pseudonoise coded signal is utilized, the result of the time convolution ofwaveform 64 with waveform 56 becomes the waveform illustrated at 62.What this means is that under normal circumstances the modulation itselfis contained within the clutter or the noise associated with theenvironment.

The desired data is extracted by the time convolution of the pseudonoise encoded preamble for the data message with waveform 54, with thepreamble preceding the data stream. This known preamble is resident inthe radar's signal processor and is designed to extract the message fromthe tag on the up link. This preamble is also resident in the tag. Timeconvolution of the two waveforms the results in the extraction of thedata.

Referring to FIG. 8, what will be seen is that to the external world thedata message, here illustrated at 66, has an amplitude which is muchless than the amplitude of the radar spectrum, with the graphs of FIG. 8being in the frequency domain. Thus, the relative amplitude of the radarfrequency spectrum 68 is orders of magnitude higher than that of thedata message.

Referring to FIG. 9, in the past there has been a need to provide avariable tap convolver to match the bandwidth of the variousinterrogating radars or other interrogating signals. Thus, for instance,assuming an X-band interrogating radar signal were to be utilized with aparticular chirp rate and a particular pulse repetition interval, thenthe variable tap convolver needed to be set for this particularinterrogating waveform. Since there is a possibility of numerousdifferent types of interrogating waveforms, the variable tap convolverneeded to be quite large and was both expensive and consumed largeamounts of power. Moreover, the convolving capability with a variabletab convolver was limited to that which was initially designed into theconvolver itself.

In an effort to provide a universal convolver which can operateregardless of the characteristics of the incoming waveform, a fixed tapconvolver 70 is used which is preceded by a decimater 72, the purpose ofwhich is to throw away samples which are generated by a sampling devicesuch as a sampling analog-to-digital converter 74. This sampling A/Dconverter is driven by a clock 76 at a frequency F_(s) which is muchgreater than the bandwidth of the incoming signals.

For instance, the frequency of the clock might be in the 800 MHz range,whereas the Nyquist frequency of the interrogating signal would be inthe 20 to 50 MHz range.

It is the purpose of the decimater to throw away unused samples suchthat the sampling rate from the output of the decimater matches the rateassociated with the taps on the fixed tap convolver. Thus, the decimatermatches the bandwidth of the incoming radar signals to the fixed tapconvolver data rate. Note that the fixed tap convolver has as its otherinput, input 80 which is from the control processor so that theconvolver can convolve the data to be transmitted with the output of thedecimater.

Referring now to FIG. 10, this figure illustrates a system for directdown conversion as illustrated at 82 which takes the output fromreceiver 26 and couples it to a track and hold amplifier 82, which iscoupled to clock 76 so that the track and hold amplifier follows the RFsignal and holds its last value upon the occurrence of a so-called lastclock pulse. The purpose of this process is to provide a steady signalto analog-to-digital converter 30. The track and hold amplifier permitsthe use of a relatively slow analog-to-digital converter whichordinarily cannot directly sample a microwave signal. In this case, thetrack and hold amplifier performs a band pass sampling function, meaningthat it utilizes under sampling but preserves the modulation while atthe same time aliasing the carrier.

Referring to FIG. 11, in the frequency domain the clock pulses at F_(s),2F_(s), 3F_(s) . . . are illustrated at 84 along with the radar signal86 which when multiplied with the clock pulses produces the base bandside bands as illustrated in FIG. 12 at 88 and 90 about the DC axis 92.What is provided is direct conversion down to the base band bymultiplying the clock pulses by the radar pulse.

The use of direct down conversion results in smaller size, less powerconsumption, lower cost componentry and elimination of local oscillatorre-radiation. From a convert operations point-of-view, this is importantbecause should the tag utilize local oscillators, these localoscillators can be detected by sniffing apparatus which can locate theperson who would otherwise seek to operate in a covert manner.

Referring now to FIG. 13, the direct up conversion technique isillustrated at 100 which takes the output of convolver 70 and convertsit to an analog signal through the utilization of a conventionaldigital-to-analog converter 102. The output of digital-to-analog convert102 is applied to a return-to-zero resampler 104. The purpose of thisreturn-to-zero resampler is to track the waveform from thedigital-to-analog converter for a short period of time and then providea zero output for the longer periods of time in between. The operationof this device is described in the aforementioned patent application.

The output of resampler is optionally provided to a variable gainamplifier 106 described in U.S. Pat. No. 4,734,751 issued Mar. 29, 1988and assigned to the assignee hereof, the output of which is then coupledto a transmitter 108 in turn coupled to an antenna at 110, withtransmitter 108 providing a band pass filter function at microwavefrequencies.

As illustrated in FIG. 14, it will be appreciated that thereturn-to-zero resampler creates a pulse amplitude modulated waveform112 which is depicted to have tracked the output of thedigital-to-analog converter to a very good approximation. As can beseen, the waveform has an envelope corresponding to the applied CW sinewave from the digital-to-analog converter.

Referring to FIG. 15, the output of the return-to-zero resampler in thefrequency domain is illustrated.

Here, to either side of the sampling frequencies F_(s), 2F_(s), 3F_(s) .. . are the spectrums 114 and 116 corresponding to the output ofconvolver 70 of FIG. 13. Since the clock theoretically providesfrequencies all the way out to infinity, a band pass filter in thetransmitter is used to filter out all those clock frequencies which donot correspond to the microwave frequency of interests illustrated at118. This is done by a conventional band pass filter in the transmitterand leaves only the microwave clock frequency 120.

What will be appreciated is that the sampling frequency F_(s) used ondirect down conversion is the self-same sampling frequency which is usedon direct up conversion. The result is preservation of the spectrum ofthe returned signal.

In summary, the tag is capable of transmission upon receipt of aninterrogating waveform. For radars, this received waveform is modulatedand is transmitted in such a way that the signal is hidden in the radarground clutter. This requires the aforementioned special modulationcharacteristics and attention to spurious emission.

The tag is programmable which means it can communicate with a widevariety of radio frequency waveforms emitted from an interrogatingplatform.

Moreover, the basic technology applies to any kind of RF waveform basedon either radar or communications. The tag innovatively allows thewaveform to be stored digitally within the tag, thus enabling the tag togenerate a return that communicates with any interrogating platform.

Having now described a few embodiments of the invention, and somemodifications and variations thereto, it should be apparent to thoseskilled in the art that the foregoing is merely illustrative and notlimiting, having been presented by the way of example only. Numerousmodifications and other embodiments are within the scope of one ofordinary skill in the art and are contemplated as falling within thescope of the invention as limited only by the appended claims andequivalents thereto.

1. An RF tag comprising a programmable miniature transceiver capable ofcommunicating with a plurality of different platforms which operates byinterrogating said tag with a predetermined waveform and receiving awaveform transmitted by said tag to said platform with tag generatedinformation embedded therein.
 2. The RF tag of claim 1, wherein saidtransceiver includes a digital signal processing convolver forconvolving a digital representation of the waveform transmitted to saidtag with information to be embedded in the signal returned by saidtransceiver to the platform with which said transceiver iscommunicating.
 3. The RF tag of claim 2, wherein said information isencoded in a bi-phase pseudo random code modulation.
 4. The RF tag ofclaim 2, wherein said convolver includes a unit for direct up/downdigital conversion of the waveforms transmitted and receivedrespectively by said tag.
 5. The RF tag of claim 2, wherein theinformation to be embedded in the signal returned by said transceiverincludes a fast-time convolution modulator.
 6. The RF tag of claim 2,and further including a waveform characteristics detector coupled to thedigital representation of the waveform transmitted to said tag and aprocessor preloaded with waveform characteristics coupled to saidconvolver such that said information to be embedded is embedded into awaveform having characteristics matching those detected by said waveformcharacteristics detector.
 7. The RF tag of claim 3, wherein said unitfor direct up/down digital conversion includes an analog-to-digitalconverter for sampling the waveform transmitted to said tag and furtherincluding a clock coupled to said analog-to-digital converter, saidclock having a predetermined frequency much greater than the bandwidthof the waveform transmitted to said tag.
 8. The RF tag of claim 7, andfurther including a decimator coupled to said analog-to-digitalconverter for throwing away a predetermined number of samples therefrom.9. The RF tag of claim 8, wherein said convolver includes a fixed tapconvolver, said decimator matching the output thereof to the taps onsaid fixed tap convolver, whereby a fixed tap convolver can be usedregardless of the bandwidth of the waveform transmitted to said tag,thus to adapt said tag to a wide variety of platforms which generateinterrogating waveforms.
 10. The RF tag of claim 9, wherein the samplesthrown away by said decimator nonetheless result in a sampling rate ofthe remaining signal which is above the Nyquist rate for the waveformtransmitted to said tag.
 11. The RF tag of claim 4, wherein said directdigital down conversion unit includes a track and hold unit and a clockcoupled thereto, said track and hold unit having an input coupled to thewaveform transmitted to said tag, said track and hold unit followingsaid last-mentioned waveform and hold the last value thereof at the endof a predetermined interval established by said clock, thus to directlydown convert the frequency of the waveform transmitted to said tag. 12.The RF tag of claim 11, wherein the clock frequency of said, clock ismuch greater than the bandwidth of the waveform transmitted to said tag.13. The RF tag of claim 11, wherein said direct up conversion unitincludes a return-to-zero unit to track the waveform from said convolverfor a short period of time and then to output zero for time in between.14. The RF tag of claim 13, wherein said return-to-zero unit is clockedat the same frequency as said track and hold unit, thus not to preservethe characteristics of the waveform from said platform.
 15. The RF tagof claim 13, wherein the waveform transmitted to said tag is in themicrowave region of the electromagnetic spectrum, and further includinga band pass filter for passing only microwave signals, thus toeffectuate direct up conversion of the signal from said convolver. 16.The RF tag of claim 2, wherein said tag is placed on an individual saidtag including a geopositioning receiver for indicating the position ofsaid individual, said position being embedded into the waveformtransmitted back to said platform.
 17. The RF tag of claim 16, whereinthe amplitude of the waveform transmitted back to said platform islimited to just that above which said platform can receive, whereby,overt operation is established.
 18. The RF tag of claim 2, wherein no RFoscillators are used in said tag due to the use of said direct digitalup/down conversion, whereby said tag can be used for covert operations.19. The RF tag of claim 1, wherein said tag functions as a router. 20.The RF tag of claim 16, wherein said tag functions as a search andrescue transponder, wherein said information embedded in thetransmission back to said platform includes tag location.
 21. An RF tagcomprising a programmable miniature transceiver capable of communicatingwith a plurality of different platforms which operates by interrogatingsaid tag with a predetermined waveform and receiving a waveformtransmitted by said tag to said platform with tag generated informationembedded therein, said transceiver including a digital signal processingconvolver for convolving a digital representation of the waveformtransmitted to said tag with information to be embedded in the signalreturned by said transceiver to the platform with which said transceiveris communicating, wherein said information is encoded in a bi-phasepseudo random code modulation, and said convolver includes a unit fordirect up/down digital conversion of the waveforms transmitted andreceived respectively by said tag.
 22. An RF tag comprising aprogrammable miniature transceiver capable of communicating with aplurality of different platforms which operates by interrogating saidtag with a predetermined waveform and receiving a waveform transmittedby said tag to said platform with tag generated information embeddedtherein, said transceiver including a digital signal processingconvolver for convolving a digital representation of the waveformtransmitted to said tag with information to be embedded in the signalreturned by said transceiver to the platform with which said transceiveris communicating, wherein said information is encoded in a bi-phasepseudo random code modulation, and said convolver includes a unit fordirect up/down digital conversion of the waveforms transmitted andreceived respectively by said tag, and the information to be embedded inthe signal returned by said transceiver includes a fast-time convolutionmodulator.